The invention relates to the use of laser-welding for and a method of manufacturing by welding with a straight bead, tubular construction parts for exhaust installation, in particular in automobiles with exhaust catalyzer from austenitic or ferritic CR-steel.
It is known in the prior art to manufacture tubular construction units for such a use, and especially for exhaust pipes which are susceptible to scale formation and corrosion up to the pre or main damper from the material X5CrTi12 which is a relatively low-cost substance for this purpose. The tubular units are welded with a straight bead by WIG-welding or high frequency resistance pressure welding (H.F.) Both methods have considerable shortcomings.
After welding, the bead expansion must be removed by scraping or grinding, to an extent not detrimental to the tube shaping steps, resulting from which, for example, cold bending, flanging expanding. At wall thicknesses of 0.8-2.5 mm and tube diameters of 30 to 65 mm technical problems can arise in case of HF-welding by interior weld removal or unintentional removal which goes too deep, leading to groove fissures. It is also possible that in case of HF-welding the corresponding oxides are not completely removed and a sporadic cold welding caused by the working material can hardly be avoided. Such shortcomings in the center of the weld lead to breaking open of the weld after subsequent treatment of the tubes, like expanding or bending. This results in the production of too many low quality parts and of waste. Similar problems arise in WIG-welded tubes due to the large-grained wide structure of welding material, which structure allows only an insignificant degree of reshaping. It is difficult to attain through-welding at the inside. Due to this outside inside effect only small reshaping is possible upon reshaping during processing of the tubes.
In connection with the development of ceramics-lines motors with hotter exhaust gases it makes sense to manufacture the exhaust installations from two-layer materials, which have for example an outer layer of ferritic and an inner layer of austenitic material.